linux-kernel - Re: [PATCH] xen-swiotlb: exchange memory with Xen only when pages are contiguous

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Message-ID: <3e65208c-cb11-d918-00eb-012a97e56fec@oracle.com>
Date:   Mon, 29 Oct 2018 19:51:51 -0700
From:   Joe Jin <joe.jin@...cle.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     "DONGLI.ZHANG" <dongli.zhang@...cle.com>, konrad@...nel.org,
        Christoph Helwig <hch@....de>,
        John Sobecki <john.sobecki@...cle.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-kernel@...r.kernel.org\"" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen-swiotlb: exchange memory with Xen only when pages are
 contiguous

On 10/25/18 11:56 AM, Joe Jin wrote:
> I just discussed this patch with Boris in private, his opinions(Boris,
> please correct me if any misunderstood) are:
> 
> 1. With/without the check, both are incorrect, he thought we need to
>    prevented unalloc'd free at here. 
> 2. On freeing, if upper layer already checked the memory was DMA-able,
>    the checking at here does not make sense, we can remove all checks.
> 3. xen_create_contiguous_region() and xen_destroy_contiguous_region()
>    to come in pairs.
I tried to added radix_tree to track allocating/freeing and I found some
memory only allocated but was not freed, I guess it caused by driver used
dma_pool, that means if lots of such requests, the list will consume lot
of memory for it. Will continue to work on it, if anyone have good idea
for it please let me know, I'd like to try it.

Thanks,
Joe